Article

Abundance analysis of prime B-type targets for asteroseismology I. Nitrogen excess in slowly-rotating beta Cephei stars

Astronomy and Astrophysics (Impact Factor: 5.08). 07/2006; DOI: 10.1051/0004-6361:20065171
Source: arXiv

ABSTRACT We present the results of a detailed NLTE abundance study of nine beta Cephei stars, all of them being prime targets for theoretical modelling: gamma Peg, delta Cet, nu Eri, beta CMa, xi1 CMa, V836 Cen, V2052 Oph, beta Cep and DD (12) Lac. The following chemical elements are considered: He, C, N, O, Mg, Al, Si, S and Fe. Our abundance analysis is based on a large number of time-resolved, high-resolution optical spectra covering in most cases the entire oscillation cycle of the stars. Nitrogen is found to be enhanced by up to 0.6 dex in four stars, three of which have severe constraints on their equatorial rotational velocity, \Omega R, from seismic or line-profile variation studies: beta Cep (\Omega R~26 km/s), V2052 Oph (\Omega R~56 km/s), delta Cet (\Omega R < 28 km/s) and xi1 CMa (\Omega R sin i < 10 km/s). The existence of core-processed material at the surface of such largely unevolved, slowly-rotating objects is not predicted by current evolutionary models including rotation. We draw attention to the fact that three stars in this subsample have a detected magnetic field and briefly discuss recent theoretical work pointing to the occurrence of diffusion effects in beta Cephei stars possibly capable of altering the nitrogen surface abundance. On the other hand, the abundances of all the other chemical elements considered are, within the errors, indistinguishable from the values found for OB dwarfs in the solar neighbourhood. Despite the mild nitrogen excess observed in some objects, we thus find no evidence for a significantly higher photospheric metal content in the studied beta Cephei stars compared to non-pulsating B-type stars of similar characteristics. Comment: Accepted for publication in A&A, 21 pages, 7 figures

0 Bookmarks
 · 
111 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The eclipsing and double-lined spectroscopic binary system V453Cygni consists of two early B-type stars, one of which is nearing the terminal age main sequence and one which is roughly halfway through its main-sequence lifetime. Accurate measurements of the masses and radii of the two stars are available, which makes a detailed abundance analysis both more interesting and more precise than for isolated stars. We have reconstructed the spectra of the individual components of V453Cyg from the observed composite spectra using the technique of spectral disentangling. From these disentangled spectra, we have obtained improved effective temperature measurements of 27900 +/- 400 and 26200 +/- 500K, for the primary and secondary stars, respectively, by fitting non local thermodynamic equilibrium theoretical line profiles to the hydrogen Balmer lines. Armed with these high-precision effective temperatures and the accurately known surface gravities of the stars we have obtained the abundances of helium and metallic elements. A detailed abundance analysis of the primary star shows a normal (solar) helium abundance if the microturbulence velocity derived from metallic lines is used. The elemental abundances show no indication that CNO-processed material is present in the photosphere of this high-mass terminal age main-sequence star. The elemental abundances of the secondary star were derived by a differential study against a template spectrum of a star with similar characteristics. Both the primary and secondary components display elemental abundances which are in the ranges observed in the Galactic OB stars.
    Monthly Notices of the Royal Astronomical Society 01/2009; 394:1519-1528. · 5.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The recent downward revision of the solar CNO photospheric abundances now leads to severe inconsistencies between theoretical models for the Sun's internal structure and the results of helioseismology. There have been claims that the solar Ne abundance may be underestimated and that an increase in this ill-defined quantity could alleviate (or even completely solve) this problem. To address the validity of this hypothesis, we present a fully homogeneous non-LTE abundance analysis of the optical Ne I/II lines in a sample of 18 nearby B-type stars. Our very preliminary results point towards a mean neon abundance slightly higher than the new solar value, but apparently insufficient by itself to restore the agreement between the solar models and the helioseismological constraints.
    11/2007;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: By applying systematically enlarged multi-configuration Dirac-Fock wavefunction, the transitions for electric-dipole allowed (E1) and forbidden (E2, M1 and M2) lines are studied among 4f pair coupling and low-lying configurations for singly ionized nitrogen. Most important effects of relativity, electron correlation, the rearrangement of electron density, Breit interaction, and quantum electrodynamic effects are included in the computation. Then, allowed (E1) and forbidden (E2, M1 and M2) transition probabilities of 4f for N+ are obtained and compared with experimental results. Good agreement with available experimental results is found and most of the data of 4f are presented for the first time.
    Chinese Physics B 01/2010; 19(5). · 1.15 Impact Factor

Full-text (2 Sources)

Download
1 Download
Available from